1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Typically, magnetic heads for perpendicular magnetic recording have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate, as is the case with magnetic heads for longitudinal magnetic recording. The write head includes a pole layer that produces a magnetic field in the direction perpendicular to the plane of the recording medium. The pole layer includes, for example, a track width defining portion having an end located in a medium facing surface that faces toward the recording medium, and a wide portion that is coupled to the other end of the track width defining portion and that is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the write characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, suffer degradation. It is therefore required to achieve better write characteristics with decreasing track width. Here, the length of the track width defining portion taken in the direction perpendicular to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
However, as the neck height gets smaller, it becomes difficult to precisely define the track width. The reason is as follows. It is difficult to precisely form a portion of the side surface of the pole layer near the boundary between the track width defining portion and the wide portion. It is therefore likely that the portion of the pole layer near the boundary between the track width defining portion and the wide portion has such a shape that the width gradually increases with increasing distance from the medium facing surface. As a result, as the neck height gets smaller, it becomes difficult to precisely define the width of the end of the track width defining portion located in the medium facing surface, that is, the track width.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits a better capability of writing on a recording medium compared with the longitudinal magnetic recording system, if the above-mentioned skew occurs, there arise problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this is hereinafter called adjacent track erasing), or unwanted writing performed between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
As one of techniques for preventing the problems resulting from the skew described above, there is known a technique in which the end face of the track width defining portion located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in U.S. Patent Application Publication No. US2003/0151850 A1 and U.S. Pat. No. 6,504,675 B1, for example. For magnetic heads, typically, in the medium facing surface, the end farther from the substrate is located forward along the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the shape of the end face of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is shorter than the side farther from the substrate.
As a magnetic head for perpendicular magnetic recording, there is known a magnetic head including a shield, as disclosed in U.S. Patent Application Publication No. 2005/0219747 A1, for example, wherein the shield has an end face located in the medium facing surface at a position forward of the end face of the pole layer along the direction of travel of the recording medium with a predetermined distance provided therebetween. A gap layer made of a nonmagnetic material is provided between the pole layer and the shield. The shield has a function of preventing a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and expanding in directions except the direction perpendicular to the plane of the recording medium. A magnetic head including such a shield enables a further improvement in recording density.
U.S. Patent Application Publication No. US2002/0034043 A1 discloses a technique in which a portion of the pole layer (the main pole) located near the medium facing surface is made to have a thickness that decreases with decreasing distance from the medium facing surface.
To solve the problems resulting from the skew, it is also effective to reduce the thickness of the track width defining portion taken in the medium facing surface. If the entire pole layer is made thin, however, a cross-sectional area of the pole layer perpendicular to the direction in which magnetic flux flows is reduced. As a result, the pole layer becomes unable to introduce magnetic flux of great magnitude to the medium facing surface, and this leads to degradation of overwrite property.
To cope with this, as disclosed in U.S. Patent Application Publication No. US2002/0034043 A1, a portion of the pole layer near the medium facing surface can be made smaller in thickness than the other portion of the pole layer. It is thereby possible to reduce the thickness of the track width defining portion taken in the medium facing surface and to introduce magnetic flux of great magnitude to the medium facing surface through the pole layer. In this case, however, the following problem can occur. That is, according to the technique described above, it is inevitable that the pole layer has a portion in which the thickness abruptly changes when seen in a direction perpendicular to the medium facing surface. In the portion in which the thickness abruptly changes, flux leakage from the pole layer is likely to occur. If the portion in which the thickness abruptly changes is close to the medium facing surface, magnetic flux leaking from this portion reaches the medium facing surface and further leaks to the outside from the medium facing surface. As a result, the effective track width can increase and the foregoing problems resulting from the skew can occur.
In the magnetic head disclosed in U.S. Patent Application Publication No. 2005/0219747 A1, a surface of the pole layer closer to the shield has a tapered surface portion. In this magnetic head, the point at which the tapered surface portion starts, when seen from the medium facing surface, is located away from the medium facing surface. A portion of this surface of the pole layer closer to the shield, the portion extending from the medium facing surface to the point at which the tapered surface portion starts, is perpendicular to the medium facing surface. As a result, when seen in the direction perpendicular to the medium facing surface, a region of the pole layer from the medium facing surface to the point at which the tapered surface portion starts has a uniform thickness, while a region of the pole layer from the point at which the tapered surface portion starts to the point at which the tapered surface portion terminates has a thickness that increases with increasing distance from the medium facing surface.
Here, a consideration is given to a magnetic head in which the pole layer has: a first portion having a uniform thickness and including a first end located in the medium facing surface and a second end located away from the medium facing surface; and a second portion coupled to the second end of the first portion and having a thickness greater than that of the first portion. An example of such a magnetic head is the one disclosed in U.S. Patent Application Publication No. 2005/0219747 A1.
In the case where the pole layer has the first portion and the second portion described above, the cross-sectional area of the pole layer perpendicular to the direction in which magnetic flux flows is smaller in the entire first portion. Consequently, if the distance from the medium facing surface to the boundary between the first and the second portion is great, the pole layer is unable to introduce magnetic flux of great magnitude to the medium facing surface. On the other hand, if the distance from the medium facing surface to the boundary between the first and the second portion is small, a problem described below can occur. First, note that the distance from the medium facing surface to the boundary between the first and the second portion can vary due to a variation in the position of the boundary between the first and the second portion that can occur when the pole layer is formed, and/or due to a variation in the position of the medium facing surface that can occur when the medium facing surface is formed by polishing. Here, the distance from the medium facing surface to the boundary between the first and the second portion has an influence on write characteristics. If the distance from the medium facing surface to the boundary between the first and the second portion is small, a slight variation in this distance would cause a great variation in write characteristics.
For the foregoing reasons, conventionally, it has been difficult to prevent the problems resulting from the skew and to improve the write characteristics.